1. Field of the Invention
The present invention relates to a method of brazing relatively small components of precision devices, instruments and equipment such as ink-jet printers and various audio devices.
2. Discussion of the Related Art
In the field of office automation devices and audio-video devices, efforts to reduce the size and weight of the devices have been made at an accelerated pace, and there have been increasing needs of reducing the size and improving the precision (e.g., dimensional accuracy), of the components incorporated in such devices. For instance, an ink-jet printer widely used as an output device of a computer is equipped with an ink-jet print head of a structure having nozzles in the form of minute holes of 30-50 .mu.m diameters, and ink passageways and chambers whose cross sectional dimensions range from several tens to several hundreds of microns, for example.
For forming such small-sized nozzles, passageways and chambers of the ink-jet print head with high dimensional accuracy, a plurality of thin metallic planar members or plates are formed with various holes, windows, apertures and any other openings by suitable techniques such as etching, pressing and punching utilizing photolithography. These metallic plates are bonded together into an integral structure which has internally defined ink passageways and chambers corresponding to the openings, and externally open nozzles corresponding to the holes.
In the conventional manufacture of an ink-jet print head constructed as described above, the metallic plates are bonded together, usually by an organic or inorganic adhesive or bonding agent, which is suitable for assuring high sealing or tightness to an ink. This bonding using an adhesive suffers from easy flow, spreading or dislocation of the adhesive beyond the intended bonded portions of the plates toward the ink passageways, etc., whereby the passageways and other open spaces within the head structure tend to have deviations from the nominal shapes, leading to deterioration of the quality of the ink-jet print head. When an organic adhesive is used, in particular, the holes and other openings formed through the metallic plates are likely to be plugged or partially filled with the adhesive. In this case, the produced print head does not normally function, and the yield ratio of the products is considerably lowered. On the other hand, an attempt to reduce the amount of the adhesive for avoiding the above problem leads to another problem, namely, increased possibility of bonding failure at local portions of the metallic plates, which results in lowering the fluid tightness or sealing with respect to the ink.
To solve the above problems, there have been proposed the following methods, which include by way of example:
(1) Using a magnetic material for metallic plates, so that the plates are secured to each together by a magnetic force; PA1 (2) Interposing a mass of a magnetic fluid between bonding surfaces of metallic plates, for improving the sealing with respect to the ink; PA1 (3) Injection-molding a plastic: plate with necessary ink passageways and chambers, within a mold in which metallic plates are positioned in place, so that the metallic plates are bonded to the plastic plate, concurrently with the formation of the plastic plate, to thereby form an integral structure; and PA1 (4) using plastic materials for all plates constituting an integral structure, with an organic solvent applied to the bonding surfaces of the plastic plates, so that the plastic plates are bonded together under pressure, with the plastic materials near the bonding surfaces dissolved by the organic solvent.
However, the above methods all suffer from another problem such as increased costs of the material or the production facility, or deterioration of the dimensional accuracy and strength due to the use of plastic materials. Thus, the proposed solutions are not practically satisfactory, for economically producing a high-quality ink-jet print head.
There have been some attempts to bond metallic plates by an ordinary brazing process, which usually employs a brazing material which has a comparatively high degree of wettability with respect to the metallic plates, to assure satisfactory bonding of the plates. In this case, the brazing material tends to spread easily beyond the intended bonding areas, leading to detrimental plugging or closing of the nozzles. On the other hand, the use of a brazing material having a relatively low degree of wettability to the metallic plates results in difficult application of the brazing material so as to assure uniform thickness over the entire area of bonding of the plates. In this case, the produced print head may suffer from poor or incomplete sealing of pumping chambers, for example, due to local bonding failure or defects, which leads to leakage of the pressurized ink. Alternatively, the print head may have an air gap between the bonding surfaces, which causes air trapping in the air gap and a pressure loss in the pumping chambers, causing undesired ink jetting characteristics of the print head.
Recently, a brazing technique, so-called "vacuum brazing" at a sub-atmospheric pressure finds various applications in the field of bonding of small precision components. It is generally recognized that this vacuum brazing technique permits the manufacture of an ink-jet print head as described above, with high accuracy without problems such as plugging of the nozzles, even when the metallic plates are bonded together by a brazing material which has a comparatively high degree of wettability with respect to the metallic plates.
However, the vacuum brazing process requires a large-sized, expensive vacuum heating furnace to melt the brazing material, inevitably resulting in an extremely high cost of manufacture of the print head, as compared with the cost where an ordinary brazing process is utilized.